N. meningitidis is a non-motile, Gram-negative human pathogen that colonises the pharynx and causes meningitis (and, occasionally, septicaemia in the absence of meningitis). It causes both endemic and epidemic disease. Following the introduction of the conjugate vaccine against Haemophilus influenzae, N. meningitidis is the major cause of bacterial meningitis in the USA.
Based on the organism's capsular polysaccharide, various serogroups of N. meningitidis have been identified. Serogroup A is the pathogen most often implicated in epidemic disease in sub-Saharan Africa. Serogroups B and C are responsible for the vast majority of cases in the United States and in most developed countries. Serogroups W135 and Y are responsible for the rest of the cases in the USA and developed countries. After serogroup, classification includes serotype, serosubtype and then immunotype, and the standard nomenclature lists serogroup, serotype, serosubtype, and immunotype, each separated by a colon e.g. B:4:P1.15:L3,7,9. Within serogroup B, some lineages cause disease often (hyperinvasive), some lineages cause more severe forms of disease than others (hypervirulent), and others rarely cause disease at all. Seven hypervirulent lineages are recognised, namely subgroups I, III and IV-1, ET-5 complex, ET-37 complex, A4 cluster and lineage 3. These have been defined by multilocus enzyme electrophoresis (MLEE), but multilocus sequence typing (MLST) has also been used to classify meningococci [ref. 1].
A polysaccharide vaccine against serogroups A, C, W135 & Y has been known for many years [2, 3] but a vaccine against serogroup B has proved elusive. Vaccines based on outer-membrane vesicles have been tested [e.g. see ref. 4], but the protection afforded by these vaccines is typically restricted to the strain used to make the vaccine. There remains a need, therefore, for a broadly-effective serogroup B vaccine.
Genome sequences for meningococcal serogroups A [5] and B [6,7] have been reported, and the serogroup B sequence has been studied to identify vaccine antigens [e.g. refs. 8 to 13]. Candidate antigens have been manipulated to improve heterologous expression [refs. 14 to 16].
It is an object of the invention to provide further and improved compositions for providing immunity against meningococcal disease and/or infection, and in particular for providing broad immunity against serogroup B meningococcus.